This invention relates to subcutaneously implanted infusion devices and in particular to a filter system for such devices.
Subcutaneous infusion devices are totally implantable and are designed to provide repeated access to a body space such as the vascular system. They typically include an injection chamber accessible through a septum, the injection chamber being connected by an exit port and catheter to the desired body space. The device is implanted just beneath the skin, and the injection chamber may be accessed repeatedly by passing a needle through the skin and septum.
One such device is known as an infusate pump. An infusate pump has a relatively large reservoir for storing a supply of medicament. The medicament is pumped from the reservoir to the desired body space at a selected rate. To avoid having to operate on a patient to remove the infusate pump to refill it periodically, the reservoir is accessible through a septum in the wall of the implanted infusate pump.
Another such device is an injection port. An injection port typically includes a relatively small injection chamber accessible through a septum and in direct fluid communication with a body space. The medicament delivered to the injection chamber of the implanted port flows immediately to the body space. Fluid also may be withdrawn from the injection chamber. Injection ports may be very small, as for example the low-profile microinjection port described in the commonly-owned co-pending patent application of even date and entitled MICROINJECTION PORT, Ser. No. 07/151,406.
It is desirable to use a filter in an implantable subcutaneous infusion device to prevent particles introduced into the device's chamber from entering into the body space accessed by the chamber. For example, particles of fat, skin, dust, rubber and plastic sometimes are introduced into the injection chamber of the device as a needle is passed into and through the skin and septum to access the chamber. Such particles may pose a serious danger to the patient, which danger is of increased concern in pediatric patients whose relatively smaller body passages may become blocked more easily than the larger passages of adults.
Conventional membrane-type filters are of limited usefulness in infusion devices. They suffer from questionable compatibility with many of the drugs and fluids that must be delivered; they also may tear or be pierced by a needle. Alternatives to membrane-type filters include filter elements such as screens or plates with small holes. However, manufacturing, manipulating, and attaching such small separate filter elements can be problematic, especially when manufacturing a filter for a low profile device, such as the micro-injection port described in the previously mentioned, commonly owned, co pending patent application.